Hitherto, as the one-way clutch using a sprag, a one-way clutch has been known, wherein a plurality of cam surfaces respectively put into contact with an outer circumferential surface of an inner ring and an inner circumferential surface of an outer ring, a cage in which a plurality of pockets for accommodating individual sprags are formed in order to regulate the mutual circumferential positions of the plurality of sprags, and a ribbon spring that has pockets formed to respectively accommodate the sprags and that urges the sprags in a direction in which each of the inner ring and the outer ring is locked are arranged in an annular space formed between the inner ring and the outer ring. Further, it has been also known that the higher the hardness of each of the sprags and the inner and outer rings becomes, the abrasion resistance of the one-way clutch is enhanced. In the case of a one-way clutch of this type, sometimes, lubrication is performed using a lubricant that contains a friction adjusting agent. For example, a one-way clutch for use in an automobile starting device (starter) utilizes engine oil as lubricating oil. Recent engine oil contains a friction adjusting agent (molybdenum) for reducing friction.
Patent Document 1: JP-A-2001-330062